The invention is related to a method for producing wire connections between a first connection point located on a semiconductor chip and a second connection point located on a substrate. By means of such wire connections, the electrical connections to the integrated circuits located on the chip are made during semiconductor assembly. The second connection point of the connection can be typically located on a metallic system carrier, a so-called "lead frame" or on a different system carrier, e.g, a printed circuit with a plastic, ceramic or so-called "ball grid array" substrate, but the second connection point can also be located on a further semiconductor chip as is the case for arrangements having several chips on the same carrier ("multi-chip devices").
In accordance with generally known processes for the production of such wire connections, a wire runs through a capillary which is horizontally and vertically moveable by means of a programmable drive arrangement, which serves not only to attach the wire at both connection points but also for leading the wire between the connection points. After securing the wire to the first connection point, the capillary is always moved by the named drive arrangement to the second connection point along a predetermined trajectory on which the necessary wire length is pulled through and the wire is formed into a bridge (e.g, EP-A 0 792 716).
High demands are set on the geometry or dimensional accuracy and the mechanical stability of such wire bridges; in particular, the height of the wire loop over the surface of the chip and the substrate should generally be defined as accurately as possible and of course no touching of the edges should occur on the chip. Often numerous wire bridges leading from the chip lie close together ("fine pitch"), whereby any contact between neighbouring wires must be avoided.
A critical phase always exists at the end of the capillary movement when the capillary approaches the substrate from above, the height of which generally differs from the chip surface and exhibits some variations. It is necessary to reduce the high vertical speed of the capillary on approach. It is also known to determine the impact of the capillary on the substrate by means of a force sensor in order to completely stop the movement and to initiate the bonding of the wire to the second connection point. However, the wire first runs out under the capillary in a (smaller or larger) loop the lowest point of which touches the substrate first. Consequently, the loop is pressed flat and the wire bent sharply at the capillary and finally on bonding the wire cross-section between capillary and substrate deforms. The danger exists that on "jolting" the named wire loop the preshaped wire bridge between the capillary and the first connection point is deformed inadmissibly or is bent outwards vertically and/or laterally. Meanwhile, the wire can also be partially pushed back into the capillary, i.e, the situation is altogether difficult to master.
It is the object of the present invention to resolve the difficulties mentioned so that in series production wire bridges can be achieved in the required, programmed form with high reproduceability of the shape and with high stability.